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Shutter speeds and flash

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Shutter speeds and flash
« on: 17 / July / 2008, 18:16:13 »
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I've been experimenting with shots taken with shutter speeds adjusted manually. When flashed is used on my SD800IS, I don't think the manually set shutter speeds don't work as they should. At a setting of 1/8000, most images are completely black when the flash is turned off. With the flash turned on, images are extremely overexposed.

I don't know of a way to test the shutter speed, but I suspect that the camera uses  a slower shutter speed when the flash is used. I wanted to take some photos of water drops from a faucet with high shutter settings, but I've been unable to do this. Any suggestions?

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Offline wontolla

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Re: Shutter speeds and flash
« Reply #1 on: 17 / July / 2008, 18:43:49 »
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At a setting of 1/8000, most images are completely black when the flash is turned off.
Yes, 1/8000 is too fast for the sensor to get enough natural light. You need the flash.

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With the flash turned on, images are extremely overexposed.
Then you have to lower the flash power (possible on SD800IS?) or increase shutter speed. In case it is not enough, use something in front of the flash to block some light, like a white sheet of paper etc.

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I don't know of a way to test the shutter speed
AFAIK, no one knows. There were many experiments to calculate an "accurate" shutter speed. One of them using a spinning drill marked with chalk and measuring the angle. I don't remember the conclusions, maybe someone else does.

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but I suspect that the camera uses  a slower shutter speed when the flash is used
Actually, is the other way around, if flash is used, the camera increases shutter speed.

Re: Shutter speeds and flash
« Reply #2 on: 17 / July / 2008, 19:11:56 »
Unfortunately, I do not need any options to lower the flash power.

I took some photos at the fastest setting on my camera, 1/100k, and some images have too much light from the flash still. I believe without the help of CHDK, the camera is limited to 1/1,600. If I take the same image without setting the shutter speed manually, the image looks normal. How can it be that at a shutter speed of 1/100k set through CHDK the image is too bright with the flash turned on, but when I set the camera to full-automatic mode (with flash on), meaning the FASTEST shutter speed is 1/1,600 the camera will take normal looking photos.

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Offline fudgey

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Re: Shutter speeds and flash
« Reply #3 on: 18 / July / 2008, 01:43:37 »
Also set a narrower aperture (or if the camera doesn't have an aperture, the ND filter) by increasing Av. Higher zoom also means less light.


Re: Shutter speeds and flash
« Reply #4 on: 18 / July / 2008, 02:36:53 »
The camera does not have aperture settings. I just want to make sure that the settings I input are actually being used. I assume that if two shots that are identical expect that one is taken at 1/1,600 and the other at 1/100k, the one shot at 1/100k should be MUCH darker. However, I cannot distinguish between the photos. Is this behavior normal?

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Offline dzsemx

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Re: Shutter speeds and flash
« Reply #5 on: 18 / July / 2008, 05:04:48 »
yes is normal, because these builtin flashes are very fast (faster than 1/30000sec) and the sensor isn't that fast even if you set to 1/100000 shutter speed (eletronic shutter is not 100% effective) and mechanical shutter is far slower...

so shutter speed makes no noticeable difference, only aperture and zoom

i have an old flash (modded for syncflash) and that's really slow... around 1/500 :)
« Last Edit: 18 / July / 2008, 05:11:34 by dzsemx »

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Offline fe50

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Re: Shutter speeds and flash
« Reply #6 on: 18 / July / 2008, 05:46:15 »
It should be also helpfull to use the lowest ISO as possible, shouldn't it ?
On the Ixus series (without a aperture, only with a ND filter) the ND filter setting should be always set to "in" for high speed shutter with flash...

Re: Shutter speeds and flash
« Reply #7 on: 18 / July / 2008, 18:40:01 »
yes is normal, because these builtin flashes are very fast (faster than 1/30000sec) and the sensor isn't that fast even if you set to 1/100000 shutter speed (eletronic shutter is not 100% effective) and mechanical shutter is far slower...

so shutter speed makes no noticeable difference, only aperture and zoom

i have an old flash (modded for syncflash) and that's really slow... around 1/500 :)
What is the fastest I can expect the shutter to work?

It should be also helpfull to use the lowest ISO as possible, shouldn't it ?
On the Ixus series (without a aperture, only with a ND filter) the ND filter setting should be always set to "in" for high speed shutter with flash...
What is the difference between the In and Out setting for ND filter?


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Offline fvdk

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Re: Shutter speeds and flash
« Reply #8 on: 18 / July / 2008, 21:28:49 »
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What is the difference between the In and Out setting for ND filter?

Here is the reply i got from David (microfunguy) about the same question:

Normally, ND filter state is OFF, the Canon firmware decides if the filter is needed or not.
You can force the filter to be IN when normally it would be OUT.
For example, indoors the filter would normally be OUT.

Outdoors, the filter would normally be IN.
You can force it OUT.

To check, after setting that option, just half-press shutter (or take a photo).

This option will normally make the photo 3 stops too light or 3 stops too dark.
By selecting 'ND constant exposure', the shutter-speed is adjusted to give the correct exposure.

Theoretically, a 3 stop change should be correct but I may need to alter it slightly.

Let us say you are outdoors and exposure is 1/250 at f8.
The camera does not have an aperture, f8 indicates that the ND filter is swung IN.
Force the filter to be OUT, now the shutter-speed will be changed to 1/2000 sec !

You cannot do that with the normal camera.

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Offline dzsemx

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Re: Shutter speeds and flash
« Reply #9 on: 19 / July / 2008, 00:17:04 »
@DraGoNsLaYer786:
max shutter speed depends on other settings and sensor type, generally is around 1/20000 - 1/30000 sec
Samples: High-Speed Shutter & Flash-Sync - CHDK Wiki
« Last Edit: 19 / July / 2008, 00:25:52 by dzsemx »

 

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